SUPPLYING OF CCTV CAMERAS
This issue is rarely mentioned in descriptions of video surveillance systems, however it is frequently the main reason of improper operation of a system.
CCTV cameras are powered from 12 VDC, 24 VAC or 115/230 VAC sources.
A very popular video transmission cable in CCTV systems is CAMSET, with two power wires. CAMSET M5995
has the power wires of 0.5 mm2
intersection, whereas CAMSET 100 M6100
(indoor) and CAMSET 100 M6103_100
- of 1.0 mm2
intersection. CAMSET cables are CE certified. The coaxial part of the cables provides 92% braid coverage. Top quality of the cables is backed by 6-year warranty of the manufacturer.
Power supply from 230 VAC power line
The universally available power supply seems to be very convenient source of power. But direct connection of (suitable) cameras to 230 VAC line raise many problems connected with security of installers and users. It is necessary that all devices and cables have to meet adequate safety standards and regulations.
The equipment has to comply with CE standards.
The Marathon TS-806H outdoor housing with 230 VAC heater ( M54141
) has CE approval. It is equipped with grounding terminal that must be connected to the ground of the system.
Heaters and thermostats mounted in housings have not insulated points e.g. ends of the cables and soldering points. All installation work has to be done by highly qualified personnel, so we rather recommend to use safe 12 VDC, 24 VAC, or other low voltage systems.
Powering of cameras with 12 VDC
In CCTV installations there is often a need to use long video and power cables. Video transmission is not a problem. Our experience shows that using CAMSET M5995
cable or the version with PE sheath M5997
, it is possible to transmit video at distances 300-400 meters, with acceptable quality level. Only above 400 m an video amplifier, e.g. M1840
is required. Length problems are generally related to power supply, especially in 12 VDC systems. But the main advantage of 12 VDC systems is safety of installation work and further operation of the system.
As mentioned above, the disadvantage of 12 VDC systems is voltage drop in the wires, limiting maximum length of the lines.
Camera manufacturers show in technical specifications information about camera power supply: 12 VDC. Often they don't inform about acceptable voltage range within which the camera operates properly. Is it 11.8 V improper? Will 13 V from a car battery damage our camera?
Reliable specifications should define the maximum and minimum supplying voltage. In CCTV applications the lowest value is even more important - the minimum voltage at which the camera still works properly. We have tested a dozen various cameras and determined that the voltage at camera's terminals shouldn't drop below 11 V. Most cameras are out of order around 10.5 V. Below 11 V CCTV cameras loose colors or have problems with switching on. After further considerations, we finally have assumed 1 V as maximal acceptable voltage drop in the supplying cable.
The conductor made of stranded copper wire of 0.5 mm2 intersection at 20 oC has resistance of 39 ohm/km, another one of 1.0 mm2 intersection - 19.5 ohm/km. A typical CCTV camera consumes 150 to 250 mA. Taking the upper value, according to the Ohm's Law the maximum distance of supplying power is about 60 m for CAMSET 2x0.5 mm2, and about 120 m for CAMSET 100 2x1.0 mm2.
In the case of using outdoor housing with a 12 V heater (e.g. M5406
) the lengths decrease to around 20 m / 40 m respectively (the latter for CAMSET 100 M6100
). To extend the distances we may use power supplies with voltage adjustment, e.g. M1828
The table below illustrates maximal current that we can carry at chosen distance having concrete cable's cross-section. To prepare these calculations, voltage drop 1 V was admitted and Ohm's law used to calculate resistance according to the pattern: R=2pL/S. Where:
R - resistance of the cable (of two wires connected in the loop) [ohm]
p - resistivity of copper = 0.017 [ohm mm2/m]
L - cable length [m]
S - cable cross-section [mm2]
Table showing current carrying capacity of copper wire as the function of its length and cross-section, on the assumption that voltage drop is limited to 1V.
The table shows that a camera of 245 mA consumption can be powered via CAMSET M5997
cable at a distance of about 60 m. Using CAMSET 100 M6100
, the distance doubles to about 120 m. In the case of using outdoor set composed of u-cam 110 M1128
camera and Marathon MH-806/12 M5406
housing, its current consumption is about 900 mA. The maximum distance for CAMSET M5995
is 17 m, for CAMSET 100 M6100
- 34 m.
We can also assume that we will power a camera line with higher voltage to compensate voltage drop along the cable. However, the disadvantage of this method is unstable voltage in the case of variable load resistance (thermostat switching on and off). The voltage drop "switches" as well, and in the case of long distance the voltage increase can damage the camera. So the camera should allow the maximum voltage or has to be equipped with additional voltage regulator. For fixed loads (indoor cameras) we may use separate adjustable power supply for each camera, and set the voltage depending on the length of individual line.
Solutions for voltage drop problems in supplying cables
To power cameras we can use:
- typical 12 VDC power supplies - at short distances
- adjustable power supplies: 12-14.5 VDC
- power supply adapter ZK-40 M1830 (ca 30 V) and 12 VDC regulators at cameras (SK-40 M1831).
Example installation with adjustable power supply adapter: 12-14 V/ 2.5 A M1828
The power supply allows to power 8-10 typical ceiling or compact-type cameras with current consumption not higher than 200-250 mA. It ensures adjustment of output voltage in the range of 12-14 V, which can be used for compensation of voltage drop caused by long cables. This power supply adapter is equipped with terminal strip (six terminals) allowing easy connection of wires.
On each output there is placed fuse socket, for appropriate fuse (it has to be chosen proportionally to the load).
It is worth to use ready-made cables of 1.5 m length terminated with 2.1/5.5 DC connectors: E0695
. If the cameras are powered with cables of minimal length 10 m and maximal length 100 m, with 0.5 mm2
intersection (power supply pair of the M5995
cable), on the assumption that each cable carriers the same current of 200 mA, the voltage drop will be from 10 m x 0.1 ohm/m x 0.2 A= 0.2 V to 100 m x 0.1 ohm/m x 0.2 A = 2 V. If we power cameras with 12 VDC, the cameras get voltages from 10 V (less than typical minimum value of 11 V) to 11.8 V (within the margin). But thanks to adjustment of output voltage in the power supply adapter M1828
, we can increase the supplying voltage by about 1 V. Then we will have the voltage ranging from 11 V to 12.8 V, which means that each camera is powered with proper voltage.
The idea of using power supply adapter 12-14V/2.5A
In the case of longer distances and employing thermostats the professional solution is so called "low voltage power supply"
- it consists in using 40 VDC voltage (safe in normal conditions) - from power supply adapter ZK-40 M1830
and additional 12 V regulators SK-40 M1831
(installed at each camera).
Power supply adapter ZK-40 with 30 W transformer - M1829, or 80 W transformer - M1830, and the SK-40 M1831 regulator
Possible voltage drops related to line length and use of thermostat are eliminated by the stabilizer. We remind that voltage safe for humans in common conditions is 60 VDC and 48 VAC. Basic feature of such solution is ++safety+++, however there is also the economical aspect. The cost of stabilizers as well as of the power supply adapter (it does not need to be regulated) is the same or usually lower than of electrical AC installation with AC outlet for each camera (exactly - for the individual AC/DC adapter with regulated output). Additional advantage of this kind of low voltage supplying is the fact that all equipment can be powered from one point. This way only one UPS will be needed for backup of the whole system. Besides, the time needed for doing such installation is shorter than for mounting separate power supply adapters by each camera. The described above supply adapter M1830
allows for connection of even 16 cameras. In the case of a lower number of cameras we suggest the cheaper one: M1829
Because the stabilizers work is switched mode, the result is insensitivity to the length of the cable (e.g. 1m or 1000m) and the actual voltage drop. Power loss in the stabilizer will be approximately the same, but we should remember that together with increase of the distance the current consumed by the regulator also increases - to compensate lower input voltage. Therefore, the shorter power cables are, the lower current is absorbed from power supply, and the larger number of cameras can be powered from one transformer. For distances up to 250m, we can use 24 VAC transformer (output). For longer distances it is suggested to use 29 VAC device. Low-voltage power supply system using the described above devices allows to supply power for cameras with thermostats up to 300 m, or - without thermostats - up to 980 m. The number of cameras powered from one power supply adapter depends on thee total length of supply cables. Below we put the table showing example distances for six cases.
14 cameras w/o thermostats – 980 meters
4 cameras with thermostats – 300 meters
2 cameras with thermostats – 300 meters
4 cameras w/o thermostats – 980 meters
16 cameras w/o thermostats – 100 meters
6 cameras with thermostats – 100 meters
2 cameras with thermostats – 100 meters
10 cameras w/o thermostats – 100 meters
Powering cameras through twisted-pair cables
A similar solution to "low voltage power supply" has been developed together with employing twisted-pair cables for combined video and power transmission. We remind that in the case of signal transmission with the use of UTP/FTP cable we can use video transformer TR-1 M1663
. We use only one pair of wires then (the rest can be used for power supplying). The devices using free pairs for powering CCTV camera are TRN-1/400 M1668
transmitter (placed by the camera) and the TRO-1/400 M1669
receiver (at the monitor). The video signal is transmitted the same way as with TR-1, however the voltage is sent through the remaining pairs suitably connected in parallel, identically as in SK-40.
Economically, the use of twisted-pair cable, e.g. E1408
is the best solution - simply for the reason of low cost of the cable. Additional advantage of twisted-pair transmission is lack of electromagnetic interferences (caused e.g. by switching on and off high power machines) for the reason of differential signal transmission. Distance on which we can transmit video signal is impressive. Maximal distance of sending power supply depends on the transformer used and optional application of thermostat, as it is shown in the table below:
Summary of safety issues:
- Use safe supply voltages.
- Separate camera's zero voltage rail from the "ground".
For more expensive devices (standalone DVR, PC) consider use of additional protection devices, protecting the equipment against lightning discharges, like M1711
lighting arresters, and safety multi-outlet extension cords - P1315
Power over Ethernet (PoE)
IP cameras are often powered from PoE supplies, e.g. PSA16U-480 M1890
. They can use only one pair of wires that transmits the data and conveys power as well. The supplier complies with IEEE802.3af standard which allows to power any PoE device. The same way of power supplying is used in network devices, e.g. APs, switches etc.
PoE power supplier PSA16U-480 M1890
Chapter regarding power supply in surveillance installations has been prepared in cooperation with Delta company